Cold Definition and 394 Threads

Cold is the presence of low temperature, especially in the atmosphere. In common usage, cold is often a subjective perception. A lower bound to temperature is absolute zero, defined as 0.00 K on the Kelvin scale, an absolute thermodynamic temperature scale. This corresponds to −273.15 °C on the Celsius scale, −459.67 °F on the Fahrenheit scale, and 0.00 °R on the Rankine scale.
Since temperature relates to the thermal energy held by an object or a sample of matter, which is the kinetic energy of the random motion of the particle constituents of matter, an object will have less thermal energy when it is colder and more when it is hotter. If it were possible to cool a system to absolute zero, all motion of the particles in a sample of matter would cease and they would be at complete rest in this classical sense. The object would be described as having zero thermal energy. Microscopically in the description of quantum mechanics, however, matter still has zero-point energy even at absolute zero, because of the uncertainty principle.

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  1. D

    If you lie on the ground at night with no cover, you get cold rather

    If you lie on the ground at night with no cover, you get cold rather quickly. Much of this is due to energy loss by radiation. At night in a dry climate, the temperature of the sky can drop to -40oC. If you are lying on the ground with thin clothing that provides little insulation, the surface...
  2. S

    I'm looking for some cold propulsion possibilities

    I am coming up with a new wing suit that combines soaring with jet pack propulsion in such a way that even valley dwellers can fly, and possibly commute in this fassion. I fear compressed gas alone will not have enough thrust for long enough. One concept to think of is to charge a...
  3. Spinnor

    Why don't I always catch a cold?

    Can I assume that even though I am a bit of a germ phobe that my body is on a daily basis exposed to cold germs? I try to be careful about keeping my hands clean and not sticking them in the wrong places (mouth, nose, eyes ?). If I am constantly exposed to cold germs and I don't always get a...
  4. H

    Cold shutdown that doesn't require coolant circulation?

    "cold shutdown" that doesn't require coolant circulation? I was wondering what is preventing a plant being built that can be truly shut down and not require coolant circulation. Is it that efficiency would be reduced to unacceptable levels?
  5. G

    Does Wind Feel Cold Because of Heat Transfer?

    You now how when you feel a light breeze it feels kind of cool? Why? Atoms are moving faster and they hit your skin with higher velocity so I would think wind would be hotter than normal.
  6. M

    Condensation on a cold glass during a hot day

    Hello all. Consider the case whereby one brings out a cold drink on a hot day. Why do water droplets form on the surface of the cold glass? I would think that when water molecules in the gaseous state collide with the glass surface, they transfer some energy into the glass. Therefore by the...
  7. Q

    Will the expanding universe really end up cold and empty?

    If you take it to its extremes and space continues to expand at an accelerated rate, what happens when? 1) space is expanding so fast that virtual particles cannot annihilate. 2) if the space between quarks ends up expanding then the energy needed to pull them apart will spawn new quarks...
  8. H

    Thermal Equilibrium between a Hot and Cold Body

    Just a quick question relating to thermal equilibrium between a hot and cold body. If a hot body and cold (closed systems) are opened up to each other, the thermal energy will be transfer from the hot body to cold body through conduction. So even when thermal equilibrium is reached, the...
  9. A

    What causes metals to cold weld in a vacuum?

    I read that some metals, if sufficiently smooth, will become become cold welded upon contact in a vacuum. What process causes this?
  10. M

    Making an aluminum cold finger with LN2

    Hi, I've looked everywhere for some advice on this, I hope someone can help. We are making a cooling system for cooling thin films, and part of that setup is a liquid nitrogen-cooled cold finger. This cold finger will be inside an aluminum tube, and will move closer and farther away from the...
  11. J

    Volume of Hot & Cold water required for a known volume and temperature

    I've just set a solar thermal array for research for my thesis. I would like to simulate different usage patterns to see how the system performs. I'm doing this using a Arduino with temperature sensors at the top hot the tank and on the cold supply which will then control a motorised valve which...
  12. neduet

    Hot water is heavier than cold water.

    Hot water is heavier than cold water. If density is decreasing means its cover area is also increasing, and weight is irrelative to the area body occupies. Isn't it? W=mg, to vary the weight we have to cop with its mass and gravity. As gravity is constant then is it the mass of the water...
  13. B

    Medical Which has better health benefits, hot tea or cold tea?

    Does temperature affect the health benefits provided by drinking tea?
  14. J

    Does cold gasoline have less energy

    Driving at -30 Celsius versus driving at +25 Celsius. The gasoline has less kinetic energy at -30 Celsius... Yet our cars run fine at -30. You would think that there would be a massive difference because 60 degrees celsius difference (-30 vs +30) is a LOT of kinetic energy. Most...
  15. hxtasy

    Whats more economical, filling pot with hot water, or cold, to boil water?

    I've always wished i could figure out how to calculate this. But don't know where to start. scenario: you have to boil a liter of water. if you fill it with cold water from your faucet, it will bill in X amount of time. if you fill the water with hot water from the faucet, it will boil...
  16. P

    Light Transport in Cold Atoms? Why is this important?

    I am really not all that intelligent and fairly new to the whole mathematical equation solving thing. So please bare with me, I came to the conclusion instead of reading the daily paper I will read daily articles, as I am reading I am unfamiliar of course with the symbols being undefined in the...
  17. A

    When an object becomes very cold do the electrons stop revolving ?

    I thought that electrons revolve around the proton faster when the material is hot, and slower if it's cold, if that's not true then from where do the electrons gain the energy to constantly revolve?
  18. R

    Undergrad Research in Cold Fusion & Experiments: US Programs

    Does anyone happen to know any undergrad research programs in the U.S. that deal with cold fusion and related experiments?
  19. A

    Cold War Books & Movies: Find Your Next Read/Watch!

    I'd like some new material to devour, and I have an interest in this era for some reason, particularly the spy stuff (!) but also the space race, and other associated topics. I don't mind if it's fact or fiction really, it's not an academic pursuit. I'd quite like some books, so I can read them...
  20. V

    The taste of hot water vs. cold water

    In my chemistry class today we learned about equilibrium and how temperature affects the equilibrium constant. An example that was cited was this chemical equation: H2O <--> H3O+ + OH- I learned that increasing the heat of the water will drive the equilibrium toward the right side...
  21. C

    Cold Asphalt: Permanent Pothole Repair in a Single Step

    How do these new cold asphalts, that allow to repair potholes filled with water work? What chemistry/mechanism allows them to be so easy to manipulate at normal temperature and then rapidly solidify in a permanent road solution? I am referring to a new kind of cold asphalt, as shown in the...
  22. C

    Discover the Science Behind Cold Asphalt and How it Efficiently Repairs Potholes

    How do these new cold asphalts, that allow to repair potholes filled with water work? What chemistry/mechanism allows them to be so easy to manipulate at normal temperature and then rapidly solidify in a permanent road solution?
  23. B

    Can a Simple Cold Fusion Reactor Save Our Dying Planet?

    Okay. I'm doing a science fair project on we're kiling the Earth and that changing simple everyday things could help save our dying planet. My experiment is going to be cold fusion vs fossil fuels and to perform that experiment I need to build a simple cold fusion reactor. Anybody got any ideas...
  24. Orion1

    Gravitons and Cold Dark Matter

    What would be the distinguishing theoretical differences between gravitons with an infinitesimal rest mass (non-zero) and cold dark matter? Reference: Dark matter - Wikipedia Graviton - Wikipedia
  25. C

    Relationship between cold weather and snow

    I live in the DC metro area and we recently had snow that lasted all day (none stuck to the roads, booo). But I didnt understand that it was still snowing at well above freezing. I have a digital thermometer outside of my window and it read ~41 degrees F at its highest and never dropped below 32...
  26. T

    News Another cold war ? China and U.S.

    Like the title, has another cold war begun between China and U.S.. There are some indications and developments or Am I stating the obvious ? http://www.bbc.co.uk/news/science-environment-16423881 Appreciate comments and discussion on the topic.
  27. P

    Saponification time in Cold Process Soapmaking

    Hello everyone! I'm into home soapmaking but have no background in chemistry. I read enough about how soap is made so that I largely understand what I'm doing, but lately i got into an argument with a friend about weather or not there is still active lye in soap after ...let's say- two weeks...
  28. E

    Why Is Using a Cold Water Pipe with Running Water as a Ground More Effective?

    Why is better to use the cold water pipe as a ground for electrons?
  29. Pengwuino

    Stoopid car Stop blowing cold air

    Stoopid car! Stop blowing cold air :( So, since this is a forum full of people who knows mechanics so I figure this is the perfect place to ask this question! giggle. My car has been a pain in the butt lately. The heater blows cold air until I get the car to go over about 3k rpm. When I say...
  30. S

    Cold Fusion Experiment: Exploring Kinetic Energy

    Hi, I have a question, why wouldn't this work: Imagine you have a two large parallel plates working as a capacitor with small holes in the center of the two plates. You put a potential over the plates. The electric field is then zero outside of the capacitor. You have Deuterium on one side...
  31. R

    Cold Rolling for Power Screw Threads: Advantages & Disadvantages

    For threading of Power screws ( like in a car jack with square/trapizoidal threading ), why is cold rolling preferred to normal material removal machining ; say turning on lathe. Or is cold rolling even preffered?
  32. M

    Cold Working Ansys: Compressive Residual Stresses Around Holes

    I have got a metal plate of aluminium. I want to put compressive residual stresses around the hole in Ansys. Can somebody guide me how can i do in ansys? any help will be appreciated. moazzam habib university of hertfordshire united kingdom
  33. U

    Rossi's E-cat and cold fusion test

    So there have been a few stories about a man named Rossi and his E-cat that can supposedly do cold fusion. My question I have is more business oriented...wouldn't a person that invented such a device prefer to keep the technology underwrap and just sell the energy than actually selling the...
  34. C

    Why does methyl cellulose dissolve in cold water but not hot water?

    I was reading about cellulose derivatives there and came across the wiki page for methyl cellulose: https://secure.wikimedia.org/wikipedia/en/wiki/Methyl_cellulose which states that it is a hydrophilic compound that dissolves in cold water but not hot water. Up until now, every compound I've...
  35. W

    Exploring Cold Fusion: Future of Energy?

    So, I was reading something today about an Italian Physicist who supposidly was able to make a cold fusion machine. It recently passed an important test and all that crap, and it will be interesting to see where it goes, but I was wondering how exactly cold fusion works? I get the jist of it...
  36. H

    Why does the weight of opened cold coke change over time?

    A bottle of coke was taken out of refrigerator. It was then kept in a sensitive weighing balance.Its cap was opened. The initial weight was found to be 2.403 kg. After a while its weight increased to 2.423 kg. Then again it started decreasing. I repeated this experiment for many times. And the...
  37. E

    Concerned that engineering might be cold and indifferent?

    I'm a freshman in college, and there's a worrying thought that's been growing in the back of my head. Perhaps it's the fact that I've just moved into a strange, new environment where my friends are gone that's making me feel off, but I wonder if I'd really enjoy engineering. I'd say I'm an...
  38. larrybud

    Can Zicam's Zinc-Based Remedy Actually Shorten the Life of a Cold Virus?

    Surprised I only found a couple of messages about Zicam, the Zinc based "cold remedy". http://www.zicam.com/ The idea is that the zinc shortens the life of the cold virus. They don't make any claims like a "cure for the common cold".
  39. C

    What is the real thing behind Cold Fusion?

    Hi guys, I have a few questions for you and I would like to know facts, because as this is a very controversial subject people might feel impelled to answer by opinions. So, What is the real thing behind Cold Fusion? What is the Science behind it? If it really works, how does it...
  40. Pengwuino

    Crave Cold Water? Refreshingly Satisfy with an Ice-Cold Glass!

    Any of you ever craved a nice glass of ice cold water? And not after any strenuous physical activity? Because I just did. God, I'm going to kill our brita filter tonight. I hope water isn't fattening.
  41. A

    Thermal - why check tire pressure when it's cold?

    Homework Statement Why should we check pressure in a tire when the tire is cold? Homework Equations ... The Attempt at a Solution After Googling around, I found a statement saying that when a tire is "cold," it means that it is at 'room' temperature, or the surrounding air in this...
  42. K

    Why do colored freezy pops turn clear when left outside in the cold?

    So this last winter, my roommates and I left a bunch of freezy pops outside to get cold fast (the temp was -20F). They were in clear plastic and may have been exposed to the sun. After about a day, we went to pick them up, and they had all turned clear. They stayed clear even when brought...
  43. W

    How are ultra cold temperatures measured?

    How are ultra cold temperatures measured? For example, sometimes I see things measured in nanoKelvins. I'm thinking there has to be direct contact since the vacuum is already hotter than this, but how is it actually done?
  44. W

    News Was Defense a lie during the Cold War?

    Was "Defense" a lie during the Cold War? Was "Defense" a lie during the Cold War?
  45. N

    How to transfer cold energy instead of heat?

    How to transfer "cold" energy instead of heat? My question is pretty basic. I am looking to radiate cold with the same concept of heat dissipation. For example on a peltier thermoelectric module gets hot on one side and cold on the other. A heatsink will help dissipate the heat from the hot...
  46. C

    Is Heat or Cold Insulation More Energy Consuming?

    Hi, guys! (I created the same thread in the Engineering topic nearly a week ago but there has been no response. So I decided to move it here. Thanks.) A few friends and I just had a discussion regarding heat and cold protection in general. Then came across a question of whether it is more...
  47. C

    Heat vs Cold Protection/Insulation

    Hi, guys! First of all, I am no physicist. I am an architect from Vietnam. A few friends and I just had an discussion regarding heat and cold protection in general. Then came across a question of whether it is more difficult and energy consuming for heat protection or for cold protection...
  48. R

    Cold Turbofan Concept (Fluid Flow Concern)

    Greetings, I recently joined this forum to get some feedback on this project I'm working and which I have searched for an answer without any luck. My goal is to get the most airflow velocity in an outlet of a ducted fan. I'm using a 20,000RMP fan that is pushing air from a ~1.25" inlet to...
  49. Q

    Is the Wave Function of a Super Cold Gas Different than at Higher Temperatures?

    Consider a super cold gas tube (of, say, hydrogen), is the wave function of the gas different than at a higher temperature? How about for a lone electron within the gas?
  50. O

    Heat & Cold: Atomic Level & Beyond

    What is heat and cold in the atomic scale? Why do things sometimes feel hot and sometimes cold?
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